Thermal processing is one of the most important methods mankind has developed for extending the storage life of perishable foodstuffs. However, the thermal process causes some destruction of the food qualities. Nutritional value, texture, color and flavor are usually damaged to a greater or lesser extent during the thermal process.
The soft texture of most canned vegetables is recognized as a major quality defect. It is probably one of the main reasons why the sales of canned vegetables are declining while sales of fresh vegetables are increasing. Protecting food against excessive softening caused by thermal processing is an on-going problem.
VanBuren et al, J. Food Sci., 27:291 (1962), have processed snap beans using a low temperature blanch at about 170.degree. F. before canning to give a firmer-textured canned snap bean as compared to the conventional blanching at 200.degree. to 212.degree. F. The vegetable canning industry typically uses a blanch temperature of about 170.degree. F. for snap beans. Similarly, Lee et al, J. Food Sci., 44:615 (1979) have shown that a 170.degree. F. blanch gives firmer textured canned carrots.
Large quantities of vegetables and fruits are preserved by canning. This technology requires enclosing the product in hermetically sealed containers and heating at a specified temperature for a specified time to destroy all microorganisms inside the container. Products with a pH above 4.5 require a substantial heating regime to obtain commercial sterility. For example, green beans packed in brine in 1 lb cans require 22 minutes at 240.degree. F. or 13 minutes at 250.degree. F. This heavy heat treatment cannot be compromised because microorganisms of public health significance, such as Clostridium botulinum, require this degree of heat treatment to be destroyed. Unfortunately, this amount of heat causes great damage to the food texture. Most canned vegetables have a softer than desirable texture.
The present invention relates to a process for improving fruit and vegetable firmness, particularly in thermal processed foods.